Paragraph 5(5) of The Local Elections (Parishes and Communities) (England and Wales) Rules 2006 states:
"...where a casual vacancy in any such office is not required to be filled by election, the parish or community council must, as soon as practicable after the expiry of the period of 14 days referred to in paragraph (2)(c), co-opt a person to fill the vacancy."
If you have a vacancy and you have somebody willing to fill that vacancy who meets the legal requirements to be a Councillor, they should be co-opted. They still require a majority vote, but members should be reminded of their obligations under the above legislation to support the co-option, regardless of their personal views of the individual concerned.